1. Technical Field of the Invention
The present invention relates to a high-frequency device for supplying power to a load, such as a plasma processing device that performs, for example, plasma etching and plasma CVD.
2. Related Art
In the load such as a plasma processing device that performs, for example, plasma etching and plasma CVD, an impedance of the load varies every moment in accordance with progress of a manufacturing process. In order to effectively supply power to the load, it is necessary to adjust an impedance (hereinafter, it is referred to as a load side impedance ZL) on the load side seen from an output terminal of the high-frequency power supplier in accordance with variation of the load impedance Z1 (an impedance corresponding to the load). Hence, generally, not only the high-frequency power supplier for supplying the high frequency power, but also an impedance adjuster for adjusting the load side impedance ZL is combined and has been used.
In addition, a reflected wave power reaches the minimum when a power side impedance Z0 and the load side impedance ZL are matched to each other, where a power side impedance Z0 is an impedance of the power source side seen from the output terminal of the high-frequency power supplier. Additionally, an absolute value of reflection coefficient Γ reaches the minimum too. Consequently, it is possible to lower the reflected wave power by adjusting the load side impedance ZL.
There has been provided a high-frequency power supplier that adjusts the impedance by only using the impedance adjuster, but there has been also provided a variable frequency type high-frequency power supplier that can adjust the load side impedance ZL by changing an output frequency of the high-frequency power supplier in the same manner as Patent Document 1 or 2. In addition, the device including the high-frequency power supplier and the impedance adjuster is referred to as a high frequency device.
FIG. 7 is a diagram illustrating an exemplary configuration of a known high frequency device and connection relationship between the high frequency device and a load 5.
The high-frequency power supplier 50 is a system for supplying the load 5 with high frequency power through the impedance adjuster 6 and has a function of changing the output frequency.
In detail, the high-frequency power supplier 50 outputs the high frequency power by using a power amplifier 53, and high frequency power output value measured by a power meter 54 is controlled so as to reach a target value set by a power setter 56. In addition, the output frequency of the high-frequency power supplier is determined in accordance with an oscillation frequency of the oscillation circuit 52 whose oscillation frequency is controlled by the frequency control circuit 51. The high frequency power output form the high-frequency power supplier 50 is supplied to the load 5 through a transmission line 2 made of coaxial cables, an impedance adjuster 6 and a load connection portion 4 made of a shielded copper plate. In addition, an ON/OFF control circuit 57 controls an ON/OFF output of the oscillation circuit 52, and the oscillation circuit 52 outputs a high frequency signal when ON signal is being output from the ON/OFF control circuit 57. The ON/OFF control circuit 57 is controlled by manipulation of a power output switch, which is not shown in the drawing, disposed in the high-frequency power supplier 50 or by a control signal from an external device.
The impedance adjuster 6 includes reactance elements such as a capacitor and an inductor and adjusts a load side impedance ZL so that the high-frequency power supplier can adjust the reflected wave power by changing the load side impedance ZL as compared with a case where the impedance adjuster is not used. In the example illustrated in FIG. 7, the impedance adjuster includes two capacitors C1 and C2 and an inductor L1. Additionally, reactance values of the reactance elements (capacitance of the capacitor and inductance of the inductor) are fixed values obtained from data obtained by simulation or experiment in accordance with load characteristics.
The load 5 includes a processing section for performing a processing (etching, CVD, or the like) on a target subject such as a wafer, a liquid crystal substrate, or the like carried in the processing section. In the load 5, in order to process the target subject, a plasma discharge gas is injected in the processing section, the high frequency power (voltage) supplied from the high-frequency power supplier 50 is applied to the plasma discharge gas, and thus no-plasma condition is converted into a plasma condition by discharging the plasma discharge gas. Accordingly, the target subject is processed by plasma.
In the aforementioned high-frequency power supplier 50, when the output frequency is changed, the load side impedance ZL also changes, and thus it is possible to lower the reflected wave power by controlling the output frequency.
However, in some cases the reflected wave power may not be sufficiently lowered only by controlling the output frequency of the high-frequency power supplier 50. The reason is because mainly reactance component X is changed and resistance component R is little changed in the load impedance Z1 even by changing the output frequency when the load impedance Z1 is represented by Expression (1). In addition, referring to Expression (1), it is only the reactance component X that changes depending on the change in the output frequency. However, practically, the resistance component R also changes a little bit depending on the change in the output frequency, although the detailed description thereof is omitted here. In addition, in Expression (1), ‘f’ is the output frequency of the high-frequency power supplier 50, ‘C’ is the capacitance of the load, and ‘L’ is the inductance of the load.Z1=R+jX=R+j(2πfL−1/(2πfC))  (1)
In addition, there is limitation in the range of reactance component X that is changed by changing the output frequency of the high-frequency power supplier 50, and thus it is not possible to match all load impedance Z1 only by controlling the output frequency of the high-frequency power supplier 50.
Hence, the load side impedance ZL is changed by using the impedance adjuster 6 so as to lower the reflected wave power only by controlling the output frequency of the high-frequency power supplier 50.
Patent Document 1: JP-A-2006-310245
Patent Document 2: JP-A-2006-286254
The high frequency device including the high-frequency power supplier 50 and the impedance adjuster 6 can perform a control operation so as to lower the reflected wave power. However, as described above, the reactance component X is mainly changed and the resistance component R is little changed by changing the output frequency of the high-frequency power supplier. Accordingly, reactance values of the reactance elements in the impedance adjuster 6 are set in advance, so that the resistance component R becomes close to a standard value (for example, 50Ω).
However, since the load impedance Z1 varies every moment, it is not possible to make an optimum setting for every time in a manufacturing process. Hence, for example, reactance of the reactance element is previously set so that the reflected wave power is not more than the reference value in a whole manufacturing process. Specifically, the reactance element of the impedance adjuster 6 has a fixed reactance value. As described above, since the fixed reactance is preferably used in view of an increase in size of device and price, the fixed reactance is employed if possible.
However, in the case where a load has characteristics in which the load impedance Z1 greatly varies throughout the entire manufacturing process, sometimes the reflected wave power may not be sufficiently lowered and may become more than the reference value when using such a high frequency device.
To solve this problem, it can be considered to use an auto impedance matcher, instead of the impedance adjuster, capable of matching impedance by using a method of automatically controlling the variable reactance element using the variable reactance element such as a variable capacitor or a variable inductor. Specifically, the high frequency device mentioned above is configured by combining the variable frequency type high-frequency power supplier 50 with the auto impedance matcher.
However, since the auto impedance matcher controls both of the resistance component R and the reactance component X, the control operation is complicated. Moreover, when using the auto impedance matcher, size of the device and price thereof increase. In addition, when using the auto impedance matcher, there is a possibility that the control operation is unstable since the matching operation by the auto impedance matcher and the adjusting operation of the output frequency by the high-frequency power supplier 50 are performed simultaneously.
In addition, although there is a method of decreasing the reflected wave power in which only an auto impedance matcher automatically performing impedance matching not by using the variable frequency type high-frequency power supplier, but by using a high-frequency power supplier of which output frequency is fixed is used, however, a method in which the variable frequency type high-frequency power supplier is used has a time required for the adjustment for decreasing the reflected wave power shorter than that of the method in which the fixed frequency type high-frequency power supplier is used. Hence, when the adjustment speed in decreasing the reflected wave power is required, it is preferable to employ the high frequency device using the variable frequency type high-frequency power supplier.